Materials Selection, Environmental Ageing, and Circular Design of Canine Vehicle Restraint Systems: A Critical Review

Canine vehicle restraint systems are multi-material safety products in which polymer structure and condition govern energy absorption, containment, restraint, comfort, hygiene, and durability. This critical scoping review integrates materials-science studies, canine exposure studies, standards, producer data sheets, and manufacturer declarations to compare expanded polypropylene (EPP), polypropylene (PP), flexible polyurethane (PU) foams, polyamide (PA), poly(ethylene terephthalate) (PET), thermoplastic polyurethane (TPU), and glass-fibre-reinforced polymers. Quantitative comparison shows that moisture conditioning halves the yield strength of PA6, that conditioned PA6 loses 85% of its notched impact strength at −30 °C, that EPP crushing strength increases 3.45-fold between 20 and 60 kg/m3, and that viscoelastic PU foam hardens about 58-fold between 20 and −20 °C. Reproducible ageing-sensitivity and circularity classes, derived from explicit indicator thresholds, place PP/EPP and PET in the most favourable region at 1.3–2.1 USD/kg. A property-based service-life model with normalised margins, a hard-fail step function, and stated Arrhenius validity conditions is proposed and linked to dynamic safety. A Polymer Material Safety and Sustainability (PMSS) framework is compared with established methods and illustrated by an energy-absorber example. Matched dynamic testing of aged restraints is identified as the priority research need.